armillary sphere

an ancient instrument consisting of an arrangement of rings, all of which are circles of the same sphere, used to show the relative positions of the celestial equator, ecliptic, and other circles on the celestial sphere.

(är'mə-lěr'ē, är-mĭl'ə-rē) An early astronomical device made of fixed and movable rings representing circles of the celestial sphere, such as the ecliptic and the celestial equator. It was used as early as the third century BCE as both a teaching instrument and an observational tool.